Unified Dark Matter and Energy: Axions

Summary

There are various components of matter in our universe: among them
baryons, neutrinos, cold dark matter and dark energy. The nature of
some of these components is well known (baryons, neutrinos), although
the abundance might still require some explanation (e.g. through a
mechanism like baryo- or leptogenesis). The nature of dark matter and
dark energy is not understood. We thus have to answer two questions:
What is the origin of dark matter and dark energy and what are their
contributions to the current energy density?
Attempts to clarify these questions typically concentrate on any one
of these components, although one might think that they all should be
related and that the relative values of their abundances should not be
just an accident. The present project tries to explore possible
relations between the various abundances of the components of matter.
We would specifically like to investigate possible links between dark
matter and dark energy. We shall consider several possible dark matter
candidates, e.g. the axion-axino system, but also neutralinos. Axions
are known to be a possible source of cold dark matter and/or
quintessence; axinos could provide cold or warm dark matter and are in
addition closely related to the properties of the neutrino sector. The
existence of the axion-axino system is well motivated from particle
physics considerations (the strong CP problem and supersymmetry) and
they appear naturally in various unified models of fundamental
interactions such as supersymmetric grand unified theories and
superstring theories. Our investigations will be based on recent
constructions of particle physics models in the framework of string
theory that lead to an abundance of axion candidates. A thorough
understanding of the (discrete) symmetries of string theory will be
crucial for the analysis. We shall also try to analyze neutralinos
which well motivated within the MSSM. They can be either
cold or hot dark matter; only in the former case can they account for
the structure formation of the universe. In the latter case they would
be a sub-leading component of the dark matter. We consider what we can
learn about such neutralinos from laboratory experiments and ways to
distinguish them from axinos.

Role within the Transregional Collaborative Research Centre

The studies of parameter spaces and classification of DM candidates in
the present project will be of complementary relevance for A5.
Moreover, the understanding of axionic and accionic field as DE
candidates and possibly also for DM is in close connection with the
investigations done in A1. Moreover, inflationary implications of
these fields can also be exploited in the framework of A2
Observational input of crucial relevance for constraining parameter
spaces in our research will come from B3-14. Moreover, we will
benefit from DM and DE simulations from C3. More formal input on
possible sources of unified DM-DE scenarios derived from a consistent
theory of gravity, will come naturally from A3.

Further connection among the various TR33 projects are achieved
through exchange of people and joint collaborations, which will
continue in the coming years.to top